The long-term objective of this project is to develop a tumor-targeted TCR-IL2 fusion protein, ALT-801, as an immunotherapeutic for treatment of p53-positive cancers. The TCR portion of this fusion protein is specific for a peptide derived from the tumor-associated protein p53 presented in the context of HLA- A2.1. This high-affinity TCR is designed to guide the approved anti-cancer drug, interleukin-2 (IL-2), to the tumor site to enhance the IL-2 anti-tumor activity and to minimize toxicity associated with IL-2 treatment. In a number of xenograft tumor models, ALT-801 inhibited the growth or caused regression of primary tumors derived from human p53+/HLA-2.1 cancer cells and exhibited significantly better anti- tumor activity than recombinant human IL-2 alone. Mechanism-of-action studies suggest that the fusion protein binds to immune cells and guides these cells to the tumor site where they mediate their anti- tumor activities. Based on these results, ALT-801 has been advanced as a clinical candidate for the treatment of cancer patients with locally advanced or metastatic p53-positive malignancies to evaluate the safety, immunogenicity, pharmacokinetic profile and to establish the maximum tolerated dose level (MTD). The fusion protein's ability to stimulate immune cells and anti-tumor activity was also measured. Patients have been enrolled in three different dose level cohorts and the MTD has been determined. ALT-801 is well tolerated at the MTD level. Data from the treated patients also indicate that ALT-801 has a substantial longer serum half-life (i.e. ~ 3.3 hr) than that of recombinant human IL-2 and achieves the corresponding targeted serum levels. ALT-801 treatment increases serum INF3 concentration without inducing TNF1 in the patients'sera and stimulates peripheral blood mononuclear cells, indicating immune cell activation that may play a role in antitumor responses. Tumor assessment showed stable disease in approximately 50% of the treated patients with tumor shrinkage observed in some patients. Based on these findings, advancement of ALT-801 into Phase II clinical testing is warranted. Under this proposal, a Phase IIa trial will be conducted to continue the evaluation of ALT-801's efficacy and safety in the target indications where tumor responses were observed in the Phase I trial. The following specific aims will be pursued: 1) generate sufficient ALT-801 clinical material to support Phase II human clinical studies, and 2) conduct a Phase IIa human clinical trial to evaluate the efficacy and safety of ALT-801 in subjects with refractory metastatic melanoma, renal cell carcinoma, head and neck cancer and prostate cancer at the MTD dose level. Achievement of clinical endpoints proposed by this study will prompt an expansion of enrollment in the appropriate indications to provide data necessary for advancement of ALT-801 into pivotal clinical trials for FDA approval. PUBLIC HEALTH RELEVANCE: The goal of the proposed research is to examine the safety and efficacy of a novel tumor-targeted immunotherapeutic in patients with refractory metastatic melanoma, renal cell carcinomas, head and neck cancer and prostate cancer. This is a second phase of a human trial of the immunotherapeutic which has shown to provide clinical benefits for patients having these cancers. This may lead to a safe and effective approach to treat patients with refractory, metastatic cancer.